 |
| Titel |
A 10-yr Climatology of Arctic Cloud Fraction and Radiative Forcing at Barrow, Alaska |
| VerfasserIn |
Baike Xi, Xiquan Dong, Kathryn Crosby, Charles N. Long, Robert S. Stone, Matthew D. Shupe |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250034029
|
|
|
|
|
|
| Zusammenfassung |
| A 10-yr record of Arctic cloud fraction and radiative forcing has been generated using data
collected at the Atmospheric Radiation Measurement (ARM) North Slope of Alaska (NSA)
site and the nearby NOAA Barrow Observatory (BRW) from June 1998 to May 2008. The
cloud fractions (CF) derived from ARM radar-lidar and ceilometer measurements
increase significantly from March to May (0.57-0.84), remain relatively high
(~0.80-0.9) from May to October, and then decrease from November to the following
March (0.8-0.57), having an annual average of 0.76. These CFs are comparable
to those derived from ground-based radar-lidar observations during the SHEBA
experiment and from satellite observations over the Western Arctic regions. The monthly
means of estimated clear-sky and measured all-sky SW-down and LW-down fluxes at
the two facilities are almost identical with the annual mean differences less than
1.6 Wm-2. Values of LW CRF are minimum (6 Wm-2) in March, then increase
monotonically to reach maximum (63 Wm-2) in August, then decrease continuously
to the following March. The cycle of SW CRF mirrors its LW counterpart with
the greatest negative impact occurring during the snow free months of July and
August. On annual average, the negative SW CRFs and positive LW CRFs nearly
cancel, resulting in annual average NET CRF of about 3.5 Wm-2 on the basis of the
combined ARM and BRW analysis. Compared with other studies, we find that LW CRF
does not change over the Arctic regions significantly, but NET CRFs change from
negative to positive from Alaska to the Beaufort Sea, indicating that Barrow is at a
critical latitude for neutral NET CRF. The sensitivity study has shown that LW CRFs
increase with increasing cloud fraction, liquid water path, and radiating temperature
with high positive correlations (0.8-0.9). Negative correlations are found for SW
CRFs but a strong positive correlation between SW CRF and surface albedo exists. |
|
|
|
|
|
|